Electronic thread monitor for textile machines

ABSTRACT

Electronic thread monitor means for textile machines with a sensing element that is influenced directly or indirectly by the thread motion, for converting the mechanical input into electrical quantities which serve to actuate the shut-off device of the textile machine when these electrical quantities fall below a predetermined value, response value, for a predetermined time interval, shut-off threshold. The electrical quantities generated by the sensing element change the shut-off threshold inversely proportionally to the thread velocity.

United States Patent [191 Gith {45] Nov. 25, 1975 l ELECTRONIC THREADMONITOR FOR TEXTILE MACHINES Walter Gith, Monchen-Gladbach German) l75lInventor:

{73] Assignee: W. Schlat'horst 6t Cu.,

MonchemGladhuch. Germany (22] Filed: Dec. 5, I973 [ZlI Appl. No..42l,782

3.688.958 9/l972 Rydborn tttttttttt v 226" .X

Primary Examiner-Richard A. Schacher AHOrHL)" Agent, or FirmHerbert LLerner [57] ABSTRACT Electronic thread monitor means for textileHltClllllCS with a sensing element that is influenced direct! orindirectly by the thread motion, for comerting the mechanical input intoelectrical quantities which serve to actuate the shut0ff device of thetextile machine when these electrical quantities fall below a predeiermined value. response value, for a predetermined time interval, shut-offthreshold The electrical quantities generated by the sensing elementchange the shut-off threshold inversely proportionally to the threadvelocity.

5 Claims, 3 Drawing Figures US. Patent Nov. 25, 1975 Sheet 2 of23,921,877

5 A/e I w/ ELECTRDNIC THREAD MONITOR FOR TEXTILE MACHINES The inventionrelates to an electronic thread monitor for textile machines with asensing element which is in fluenced directly or indirectly by thethread motion. for converting the mechanical quantities into electricalquantities which serve for operating the shut-off device of the textilemachine if these electrical quantities exceed or fall below apredetermined value. the so-called response value, for a predeterminedtime interval. the so-called shut-off threshold.

Electronic thread monitors for textile machines. i.e.. winding machines.warping machines or cutting machines have sensing elements of the mostvaried kinds such as. for instance. optical. capacitive or piezoelectrictypes. which convert the mechanical quantities (diameter. roughness.velocity. tension, etc.) into electri cal quantities (voltage, current,frequency). The response of an electronic thread monitor occurs, forinstance. as a function of the presence of the thread. of the magnitudeof the thread tension, or of the intensity or velocity of the threadmotion. It is known that a response ofthe electronic thread monitor as afunction of the thread motion results in the shortest possible shutofftime. as the thread motion changes its state immediately if the threadis interrupted. In the case of a break of the thread, for instance, thethread velocity drops very considerably. generally to zero. In somecases. a negative thread velocity can even occur due to the tensionacting on the thread.

In those electronic thread monitors which are equipped with a sensingelement that can be influenced by the thread motion. the shut-off deviceof the textile machine is operated if the measured quantity exceeds orfalls below the response magnitude. i.e. a predetermined measurementvalue.

Particularly advantageous with respect to complexity and cost areelectronic thread monitors which derive the control from the change ofthe condition of the thread during the motion. As the thread thickness.cross section. roughness or the like are not always constant. electricalquantities of different magnitude are generated when the thread movesthrough the sensing element. These electrical quantities of varyingmagnitude are the so-called "noise signal" of the running thread. theabsence of which automatically indicates a broken thread. as the brokenthread no longer runs and therefore also cannot generate a noise signal.

n the other hand. it happens that the mechanical property of the threadwhich is used for generating the noise signal. for instance. thediameter. is constant over short lengths of the thread. This means.however. that the noise signal may become zero then also. and thissocalled noise hole simulates a broken thread.

Since. however. this noise hole is present only for a short ime. one ues in electronic thread monitors of the kind described above. as anadditional criterion for shutt ng otl' the textile machine. namely thattime interval. during which the magnitude exceeded or fell below theresponse value. As soon as this time interval reaches a predeterminedvalue. the so-called shut-0ff threshold. a thread break actually exists.However. most textile machines are run at different speeds for ditferentthreads. and the noise holes are longer. the lower the thread velocity.This leads to the need to choose the shutoff threshold relatively long.so that a 2 stopping of the textile machine due to a noise hole alone isreliably avoided. This. however. has the result in high-speed textilemachines that during the longer shut-off time. the ongoing part of thebroken thread is removed that much farther from the stopped part.

On the other hand. it may happen in textile machines that a brokenthread is taken along again by machine parts or adjacent threadsimmediately after the break and the thread motion is interrupted orreduced only briefly. so that too high a shut-off threshold does notlead to a shutdown of the machine in this case.

Particularly critical is the starting phase of the thread. i.e.. thetime until the thread has reached its normal velocity. During this phasethe noise holes also become larger and can lead to a shutdown of themachine. if the shut-off threshold is set for normal operation. withoutthe occurrence of the thread break. ln order to avoid this low speederror. one may disconnect the electronic thread monitor during a certainstarting phase. which. however. is accompanied by the disadvantage thata possible thread break during this starting phase can be detected onlyafter the end of the disconnect time, which in turn leads to thedisadvantages. already mentioned before. of a late machine shut-off.

It is a principal object of the invention to avoid the abovedisadvantages of known electronic thread monitors. According to theinvention. the solution to this problem is that the electricalquantities generated by the sensing element serve to change the shut-offthreshold interval inversely proportionally to the thread velocity. Theproportionality need not be a linear function here. but may also followan exponential function. lt is essential that the shut-off thresholdinterval and therefore. the time during which the magnitude exceeds orfalls below the response value. becomes smaller, the greater the threadvelocity. At high thread velocities even a very briefinterruption orreduction of the velocity leads to a shut-off of the textile machine,while at the low thread velocities the above-mentioned noise holes donot yet lead to crossing the shut-off threshold. The change of theshut-off threshold interval which is inversely proportional to thethread velocity. can be achieved on the one hand by providing that theelectrical quantities generated by the sensing element are alwaysinversely proportional to the thread velocity. but on the other handalso by bringing the electrical quantities which are generatedproportional to the thread velocity. into a relationship of inverseproportionality to the shut-off threshold interval.

The time constant of an electric energy storage device can serve asshut-off threshold. For instance. of a capacitor which is controlled bythe generated electrical quantities and whose adjustable charge. e.g..the charging voltage. is a measure for the response value. In thisconnection. the charging time constant as well as that for the dischargeof the energy storage device can be used as the shut-off threshold.Similarly. a maximum charge as well as a minimum charge can be a measurefor the response value.

In a particularly advantageous embodiment of the invention. thegenerated electrical quantities serve on the one hand for thepredetermined charging of the electric energy storage device. and on theother hand. for varying the time constant of the discharge circuitconnected to the energy storage device in such a manner that its timeconstant becomes smaller. the larger the value of the generatedelectrical quantity. If the electrical quantities generated by thesensing element are available in the form of electric voltages, it isadvantageous to feed these voltages first to a highpass amplifier and torectify them subsequently preferably in a full-wave rectifier. In thiscase a capacitor charged to a predetermined voltage by means of avoltage limiter, e.g., a Zener diode can serve as the energy storagedevice. In the discharge circuit of the capacitor is a controlledresistance, for instance, a transistor. whose resistance can becontrolled in relation to the output voltage of the rectifier. In thisconnection, it is furthermore possible to arrange in the control circuitof the controlled resistance :1 capacitor, whose charging voltage,determining the control voltage. is proportional to the output voltageof the rectifier via a voltage divider, so that up to reaching theshut-off threshold, the control voltage is held at a value whichprevailed shortly before the thread broke.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a particular embodiment, it is nevertheless not intended to belimited to the details shown, since various modifications may be madetherein without departing from the spirit of the invention and withinthe scope and range of equivalents of the claims.

The method of the invention. however, together with additional objectsand advantages thereof will be best understood from the followingdescription when read in connection with the accompanying drawings. inwhich:

FIG. I, is a diagram of the electric voltage corresponding to the threadvelocity during a starting operation after one second and after fiveseconds.

FIG. 2, is a block diagram of an embodiment of the invention.

FIG. 3, is a schematic diagram of the circuit of FIG. 2.

In FIG. I, the electric voltage U corresponding to the thread velocityis plotted at definite times as the curve A. Let this voltage Ucorrespond to the r.m.s. value of the noise voltage. At the points a, b,c and e will be seen voltage dips caused by the so-called noise holes,while at the point (1 a voltage drop due to a broken thread isillustrated, where the thread was taken along by other machine parts oradjacent threads immediately after the break and the voltage is therebygenerated again.

The line 8 indicates the response value, i.e., that electric voltagecorresponding to a predetermined thread velocity which, if not reached.will cause the textile machine to be shut off. As the noise holes a. h.c and e can also drop down to the voltage zero under certaincircumstances. the curve B cannot be put so low that it is reliablyinfluenced only by thread brakes. On the other hand, it can clearly beseen that for approximately the same thread velocity the noise holes c.e are considerably shorter than the voltage dip d used by brokenthreads. If one compares. for instance. the time interval e, duringwhich the voltage falls below the response value due to the noise holee. which the time interval d. during which the voltage falls below theresponse value due to the thread break 1!, the diffcrence in theintervals can clearly be seen. To obtain a unequivocal criterion betweena noise hole and a broken thread, it is therefore only necessary to makethe shut-off threshold interval correspondingly large.

On the other hand. the left part of FIG. I shows also how at lowervelocities and therefore. lower voltages, the time interval u for thenoise hole a is of the same order of magnitude as the time interval dfor the case of a thread break d. This means that in this velocity rangethe machine is shut off by a noise hole corresponding to the hole a. Inorder to avoid this shortcoming, known electronic thread monitors aredisconnected during this velocity phase.

The present invention is based on the discovery that the disadvantagesdescribed of known electronic thread monitors can be avoided if it ispossible to change the time interval determining the shutting-off of thetextile machine with the velocity. According to the invention. this canbe achieved by the provision that the electrical quantity generated bythe sensing element. i.e., the voltage according to curve A, serves tochange the shut-off threshold in inverse proportion to the threadvelocity. The time interval, during which the voltage must fall belowthe response value according to curve B to effect the shut-down of thetextile machine, should therefore be longer, the lower the threadvelocity, and it is to become increasingly shorter with increasingthread velocity. While in the case of the righthand region of the timescale in FIG. I the shut-off threshold leading to the shutdown of thetextile machine is about 20 msec, the shut-off threshold should beconsiderably longer at the lower velocities corresponding to theleft-hand region of the time scale. as the thread velocity isconsiderably lower. If one has, for instance, at the thread velocityaccording to that of the noise hole a, which is lower by aboutone-third, a shutoff threshold of msec instead of 20 msec, it will beseen clearly that the noise hole a cannot lead to a shutdown of thetextile machine.

A particularly advantageous example of an embodiment of the inventionwill be explained with reference to the block diagram shown in FIG. 2.

The thread 1 to be monitored runs through the sensing element 2 as inall present electronic thread monitors. The noise signal present in theform of an AC voltage is fed to a highpass amplifier 3, so that thesignal becomes larger and larger with increasing thread velocity. Afterthe full wave rectifier 4 and the amplifier 5 following it, therectified voltage is fed on the one hand to a voltage limiter 6, and onthe other hand, to an analog storage device 7. The limited voltage from6 is connected to a shut-off delay storage device 8, whose shutoff delaycorresponds to the shut-off threshold and is controlled by the voltageof the storage device 7 in an inversely proportional manner. When theshut-off delay time has run out and the shut-off threshold has thus beenreached, the buffer and threshold-value amplifier 9 triggers via the busI0 the thyristor switch II, which excites the stop magnet I2 of thetextile machine drive. After the thread break is repaired, the circuitll, l2, l3, I4 is re-energized by the key 13 when the textile machine isstarted up.

FIG. 3 shows an example of an embodiment of the circuit parts 6, 7 and 8according to FIG. 2. The limiter 6 consists of the resistor 6a, theZener diode 6b and the diode 6c. The analog storage device 7 consists ofthe resistors 70, 7h. 72. the diode 7c and the capacitor 7d. Theshut-offdelay memory 8 is composed of the capacitor 80. which can bedischarged with constant current via the transistor 8a and the resistor8b.

The amplifier 5 supplies a positive output voltage. which corresponds tothe thread velocity and is divided down to a desired magnitude by meansof the resistors 70, 7b and 7e. At the same time, the voltage behind thediode 6c is limited by the Zener diode 6b to a constant magnitude. whichis stored in the capacitor 8c. The transistor 81: is. together with theresistor 8/2. on the one hand an impedance transformer for the memory 7and. on the other hand. a linear discharge resistor for the capacitor81.

in the event of a break in the thread. the DC output voltage of theamplifier 5 breaks downv Thereby. the capacitor 8(' can discharge viathe transistor 8a and the resistor 8b. as long as the voltage present atthe base of the transistor 8a permits. So that the transistor 8a withthe resistor 8b can constitute a constant-current load for the capacitor8c. the base voltage must therefore be made available long enough. Tothis end. the time constant of the capacitor 7d. discharging via thetransistor 8a and the resistor 8b. must be made about 40 times longerthan that of the capacitor 80. This means that the magnitude of thedischarge current for the capacitor 8c. constant during the dischargetime. depends on the magnitude of the voltage stored in the capacitor7d. Thereby. the last thread velocity prior to the voltage dip due to abreak of the thread or a noise hole determined the discharge time of thecapacitor 8c in such a manner that a high thread velocity results in ashort discharge time and therefore, a low shut-off threshold or a shortresponse time of the stopping magnetic relay 12. Conversely. a lowvoltage at the capacitor 7d prior to the breakdown of the voltagesupplied by the amplifier 5 causes a slow discharge of the capacitor 8cand therefore. a high or longer shut-off threshold.

It is not absolutely necessary that the capacitor 8c is completelydischarged. Instead. the switching threshold of the amplifier 9 can beset so that at an accurately fixed partial discharge of the capacitor 8cthe amplifier responds, for instance, to a reduction of the chargingvoltage to to The operating point of the DC voltage amplifier 5 ischosen in the example of the embodiment shown as high as the voltage atthe point 7f. The resistance of the resistors 7e and 7b is chosen sothat the conduction threshold of the diode 7c and the base threshold ofthe transistor 8a are balanced. At room temperature. the voltage at thepoint 7f and therefore. also the operating point of the DC voltageamplifier 5 is about I V. Any further increase of the voltage at theamplifier 5 becomes therefore effective proportionally at the emitterresistor 8b. if necessary. the point 7fvoltage can be made to track thetemperature curve of the diode 7c and the transistor 80 by a thermistor.

The example of the embodiment described abmc represents a possiblesolution with a minimum of expcnditure. which is completely sufficientfor many cases of electronic thread monitoring in textile machines.Beyond this. the use of the noise signal as the control quantity for theshut-off threshold. among other things. has further advantage that thenoise voltage is composed of the thread velocity and the threadthickness. For the same thread velocity one obtains a higher noisesignal with thick threads than with thin threads. In the rectified noisevoltage coming from the amplifier 5 are therefore contained twocomponents. which act on the shut-off delay time in the correct sense.

I claim:

I. In electronic thread monitor means for textile machines of the typehaving a sensing element influenced by the thread motion. means forconverting the mechanical quantities into electrical quantities whichserve to actuate the shut-off device of the textile machine if theseelectrical quantities exceed or fall below a predetermined responsevalue during a predetermined time shut-off threshold interval; meansresponsive to the electrical quantities generated by the sensing elementto change the shut-off threshold time interval inversely proportionallyto the thread velocity.

2. Electronic thread monitor means according to claim 1, wherein thetime constant, controlled by the generated electrical quantities. of anelectric energy storage device. whose charge is a measure for theresponse value. serves as the shut-off threshold.

3. Electronic thread monitor means according to claim 2, wherein saidgenerated electrical quantities cause a predetermined charging of anelectric energy storage device. and also vary the time constant of thedischrage circuit connected to said energy storage device. inversely tothe magnitude of the generated electrical quantity.

4. Electronic thread monitor means according to claim 3, wherein saidenergy storage device is a capacitor which is charged to a predeterminedvoltage by means ofa voltage limiter, and whose discharge circuitcomprises a controlled resistance, whose resistance can be controlled.

5. Electronic thread monitor means according to claim 4, wherein saidcontrolled resistance is controlled by a capacitor. whose chargingvoltage is proportional to the input voltage.

1. In electronic thread monitor means for textile machines of the typehaving a sensing element influenced by the thread motion, means forconverting the mechanical quantities into electrical quantities whichserve to actuate the shut-off device of the textile machine if theseelectrical quantities exceed or fall below a predetermined responsevalue during a predetermined time shut-off threshold interval; meansresponsive to the electrical quantities generated by the sensing elementto change the shut-off threshold time interval inversely proportionallyto the thread velocity.
 2. Electronic thread monitor means according toclaim 1, wherein the time constant, controlled by the generatedelectrical quantities, of an electric energy storage device, whosecharge is a measure for the response value, serves as the shut-offthreshold.
 3. Electronic thread monitor means according to claim 2,wherein said generated electrical quantities cause a predeterminedcharging of an electric energy storage device, and also vAry the timeconstant of the dischrage circuit connected to said energy storagedevice, inversely to the magnitude of the generated electrical quantity.4. Electronic thread monitor means according to claim 3, wherein saidenergy storage device is a capacitor which is charged to a predeterminedvoltage by means of a voltage limiter, and whose discharge circuitcomprises a controlled resistance, whose resistance can be controlled.5. Electronic thread monitor means according to claim 4, wherein saidcontrolled resistance is controlled by a capacitor, whose chargingvoltage is proportional to the input voltage.